1. Field of the Invention
This invention relates to a lens meter for measuring a refraction characteristic of a lens of spectacles, and more particularly to a lens judging apparatus to be used in a lens meter which automatically judges whether the lens to be measured is a lens for the right eye or left eye at the time when the framed lens of spectacles is to be measured.
2. Description of the Prior Art
A conventional lens judging apparatus of this type is disclosed in U.S. Pat. No. 4,098,002, wherein the apparatus has a lens table adapted to hold a lens to be tested and also to regulate an optical or geometric position. At the both end portions of said table surface, pressure sensitive portions each having a pressure sensitivity responding switch built therein is arranged with a space of about 1.5 times of the front length of the spectacles therebetween, so that when the lens is for the right eye, the frame for the left side lens of the spectacles pressurizes the left side pressure sensitive portion to activate the switch, and on the contrary, when the lens is for the left eye, the frame for the right side lens pressurizes the right side pressure sensitive portion to activate the switch. In this way, the prior art apparatus is designed to automatically judge which side of the lens is going to be measured from the actuation of the pressure sensitivity responding switch.
In such a conventional apparatus, however, such disadvantage is involved as that the measurer is required to constantly hold the spectacles by hand in order to pressurize the pressure sensitive portion with it, since a pressure sensitivity switch is employed and the holding of the spectacles by means of said lens receiving stand and lens table is insufficient.
Furthermore, when the measuring optical axis of the lens meter is aligned with the optical center of the measuring lens, there are some spectacles which are unable to pressure the pressure sensitive portion with the frame of a lens on the side which is not yet subjected to the alignment adjustment because of various reasons in connection with spectacles constitution such as; different configuration of the spectacles frame (particularly, the shape of the front portion thereof) refraction characteristic of a lens to be put in said spectacles frame, inter alia, characteristic of a lens as well as a prism having a specially strong spherical power, a different distance between the optical centers of the right and left lens depending on the pupillary distance of the person who puts on the spectacles. Therefore, the prior art apparatus cannot necessarily be mentioned as a perfectly automatic judging apparatus.
The present invention is accomplished in view of the above.